1. Field of the Invention
This invention relates to an on-off valve which instantly operates between an open position and a closed position. The on-off valve of this invention is particularly suitable for high-pressure fluid systems and/or those that operate with an incompressible fluid.
2. Description of Prior Art
On-off valves are commonly used to control fluid flow. There are many types of valves suitable for fluids, gas or liquid, operating at low fluid pressures. As the fluid pressure increases, the availability of suitable valves narrows. At high fluid pressures, the selection of suitable conventional valves is significantly restricted. At pressures above 10,000 psi, which are common in water jetting processes, the suitable conventional on-off and pressure-regulating valves are reduced to a few needle valves, poppet valves, stem valves, and ball valves. These valve names indicate the shape of an internal key valving element. When the water pressure is further increased to above 20,000 psi, only stem valves, needle valves, and poppet valves can withstand the high stresses induced by the pressurized fluid.
There are several reasons why high-pressure fluid, particularly water, pose problems for valves. On-off valves commonly include a valve cavity having an inlet and an outlet, an elongated valve stem having one end inside the valve cavity and an other end outside the valve cavity, a valve port shaped to mate with the internal end of the valve stem and connected to the valve outlet, and a source of outside force connected to the external end of the valve stem, as shown in FIG. 1. The outside force is used to raise or lower the valve stem so as to close or open the valve port. One common outside force is generated by a human hand working on a lever to rotate the valve stem, which is supported by threads between the valve stem and the valve body. To close the valve, the valve lever is rotated clockwise, for example, to lower the valve stem until a tip of the valve stem tightly engages the valve port. To open the valve, the valve lever is rotated counterclockwise to raise the valve stem and to open the port. Because of the hand motion involved, the valve lever generally is rotated a quarter turn at a time. If the threads around the valve stem are fine, the valve port is generally opened quite slowly. Thus the fluid will gush out of the valve port when first opened. When the fluid is water at very high pressures, severe erosion of valve stem and valve port can occur. Once eroded, a greater outside force is required to close the valve. This excessive force can deform valve parts and if so, the valve will not perform its duty. To avoid such situation, the valve port should be opened more quickly, particularly when the fluid pressure is very high and the fluid is incompressible, such as water. In other words, the on-off valve should be open or closed instantly.
Providing a fast on-off valve operation requires a linear motion on the valve stem and the slow rotation will not suffice. This linear motion can be easily applied to a valve stem at low fluid pressures. At very high fluid pressures, this task becomes very difficult. For example, a 0.125 inch diameter valve stem positioned in a valve cavity filled with 30,000-psi water will be pushed out by a force of about 368 lbf. To push this valve stem into the valve cavity, an outside force greater than 368 lbf must be applied to the external end of this 0.125 inch diameter valve stem. This force is practical if compressed air or pressurized oil is the source and is applied by an actuator, but impractical if it is applied by a hand of a human operator. Further, the strength and support of this valve stem also become critical factors. The pounding between the valve stem and its mated port is also a concern if the valve has frequent operation. As a result, there is no good conventional instant on-off valve for use with water at very high pressures. It is one object of this invention to solve these problems by providing suitable valves.
In water jetting operations, a valve must frequently interrupt the water stream. To minimize the outside force required, the diameter of the valve stem is often very small. For example, a waterjet at 55,000 psi is currently used in industrial material-cutting operations and the waterjet must be interrupted frequently with an instant on-off valve having a compressed air operated actuator. The valve stem is commonly about 0.078 inches in diameter and mates with a valve port about 0.045 inches in diameter. This diameter ratio results in a cross-sectional area of about 0.003 square inches available for generating a valve stem lifting force necessary to open the valve, if compressed air is used only in closing the valve. This valve-lifting force fades away as the valve stem and the valve port become worn. Further, the small valve port required by a small valve stem is incompatible with many water jetting processes that require high flow rates, such as cleaning ship hulls with waterjets. It is another object of this invention to provide on-off valves without such flow rate restrictions.
Another problem with conventional on-off valves used in high-pressure water jetting processes is a frequent pounding between the valve stem and the valve port. Because the valve operating force is applied directly to the valve stem and then transmitted to the valve port upon contact, failure of these two parts will occur soon if the contact is frequent. It is highly desirable to soften the contact to eliminate severe pounding of the valving parts, particularly at high fluid pressures. It is another object of this invention to provide on-off valves that have no pounding or that significantly reduce pounding of valve parts.
Automatic pressure regulating valves are very useful in pressurized fluid systems and are often a safety valve of the system. In water jetting operations, water flow is often interrupted while the pump is driven by a diesel engine that typically operates at a constant speed. Therefore, a reliable bypass valve that can sense system pressure changes and automatically bypass a predetermined amount of water to maintain a constant system pressure is of significant value. In many waterjet cleaning operations, the water flow must be interrupted frequently. Thus, the bypass valve will also be frequently operated on and off. A conventional spring-operated pressure regulating valve is illustrated in FIG. 2, which is similar in construction to the conventional manual on-off valve illustrated in FIG. 1, except that a constant outside force from a compressed spring is applied to the valve stem. The valve stem has a diameter greater than the diameter of the valve outlet port to create a cross-sectional area differential and to generate a prescribed valve lifting force Ff. When the compression spring is set against a prescribed fluid pressure Pf, the valve port is closed. When the fluid pressure is increased beyond Pf, the fluid induced force Ff is increased, thus causing the valve stem to move up and to release some fluid. As soon as the fluid pressure is restored to below Pf, the valve stem will again move down to close the valve port. This conventional setup is a main component of pressure-relief valves used in water jetting processes, despite its many known shortcomings. One serious shortcoming is the change and ultimately loss of the valve opening capability from erosion and wear of the valve stem and its mated valve seat, a situation shared by manual on-off valves.
It is one object of this invention to provide an on-off valve for use with all types of fluid, particularly incompressible fluids, at a wide range of operating pressures.
It is another object of this invention to provide an on-off valve that can be easily operated by forces generated by a human hand or foot, even at very high operating fluid pressures.
Another object of this invention is to provide an automatic valve for pressure regulating applications in high-pressure water jetting processes.